1. Field of the Invention
The present invention relates generally to a light beam scanning apparatus in an image forming system, and more particularly to a light beam scanning apparatus in an image forming system, in which a light emitting means within an image head is arranged to be perpendicular to a rotation axis of a photosensitive drum in the light beam scanning apparatus in which light beams scanned from the image head form spots on the photosensitive drum to form an image, thus simultaneously printing a plurality of lines and enabling the image to be uniform.
2. Description of the Related Art
Generally, a light beam scanning apparatus is a device for forming an image by scanning light beams to form a spot on a photoconductor medium in image forming systems, for example, a laser printer, a Light Emitting Diode (LED) printer, an electronic photocopier, a word processor machine and the like.
With the recent trend toward the miniaturization, high speed and high resolution of image forming systems, the light beam scanning apparatus has been continuously researched and developed to have characteristics of miniaturization, high speed, and high resolution to meet the trend of the image forming systems.
The light beam scanning apparatus of an image forming system is classified into a laser scanning type using an f·θ lens and an image head print type, depending on a light beam scanning manner and the construction of a light beam scanning apparatus.
FIG. 1 is a view showing a conventional laser scanning-type light beam scanning apparatus using an f·θ lens. As shown in FIG. 1, the conventional laser scanning-type light beam scanning apparatus comprises a Laser Diode (LD) 100, a collimator lens 101, a cylinder lens 102, a polygon mirror 103, a polygon mirror driving motor 104, an f·θ lens 105, an image formation reflecting mirror 106, a horizontal synchronizing mirror 108, and an optical sensor 109. The LD 100 emits a light beam in response to a video signal. The collimator lens 101 converts the light beam emitted from the LD 100 to a parallel light beam, and the cylinder lens 102 converts the parallel light beam having passed through the collimator lens 101 to a linear light beam horizontal to a scanning direction. The polygon mirror 103 scans the linear light beam having passed through the cylinder lens 102 by moving the linear light beam at a constant linear velocity. The polygon mirror driving motor 104 rotates the polygon mirror 103 at a constant velocity. The f·θ lens 105 has a certain refractive index with respect to an optic axis, and focuses a light beam on a scanning surface by deflecting a light beam with a constant angular velocity, reflected from the polygon mirror 103, in a main scanning direction and correcting aberrations. The reflecting mirror 106 reflects the light beam having passed through the f·θ lens 105 in a predetermined direction to allow the light beam to form a spot on the surface of a photosensitive drum 107, which is an image formation surface. The horizontal synchronizing mirror 108 horizontally reflects the laser beam having passed through the f·θ lens 105. The optical sensor 109 receives the laser beam reflected from the horizontal synchronizing mirror 108 and synchronizes the laser beam.
Therefore, the laser scanning-type laser light scanning apparatus is constructed so that the light beam output from the LD pass through the collimator lens to be converted to the parallel beam, the parallel beam is focused in the direction of a rotation axis of the polygon mirror by the cylinder lens and then reflected by the polygon mirror rotating at a constant angular velocity, and the reflected light beam passes through the f·θ lens and thereafter forms a spot on the photosensitive drum to have a certain radius thereof. In this case, since the resolution of a printer is determined by the radius of the spot formed on the photosensitive drum, the processing ability of the f·θ lens must be excellent.
However, in the light beam scanning apparatus, miniaturization and cost must be generally considered. Therefore, each f·θ lens is comprised of a Y-toric lens, an anamorphic lens, a free-formed surface and the like so as to reduce the number of f·θ lenses. That is, it is very difficult to process a surface of such an f·θ lens, thus deteriorating the processing ability thereof. As a result, the performance and resolution of the light beam scanning apparatus decreases.
Moreover, in order to obtain the linearity of a light beam, theta θ must be reduced. However, f must increase to reduce θ. Consequently, the laser scanning-type light beam scanning apparatus is disadvantageous in that, if f increases, the size of the light beam scanning apparatus increases, so that it is difficult to implement a miniaturized printer device.
FIGS. 2a to 2c are view showing a conventional image head print-type light beam scanning apparatus which scans light beams on a photosensitive drum using an image head.
Referring to FIGS. 2a and 2b, the light beam scanning apparatus comprises a photosensitive drum 200 and an image head 210 including a LD array 211 arranged in parallel to a rotation axis of the photosensitive drum 200.
While the image head, 210 is transferred in the direction of “S” by a transfer means (not shown), the plural LDs or LEDs provided in the image head 210 emit multiple beams in response to input video signals, and the emitted beams form a spot on the surface of the photosensitive drum 200 by a lens array, such as a minus lens and a plus lens, as shown in FIG. 2c. 
Such an image head print-type light beam scanning apparatus is advantageous in that, since the image head 210 can be arranged to be closer to the photosensitive drum 200, the light beam scanning apparatus can be miniaturized compared to the laser scanning-type light beam scanning apparatus using the f·θ lens.
However, the image head print-type light beam scanning apparatus is problematic in that, since the image head is arranged in parallel with the rotation axis of the photosensitive drum, a printing speed depends on a transfer speed of the image head, so that the printing speed becomes lower than that of the laser scanning-type light beam scanning apparatus using the f·θ lens. Further, the image head print-type light beam scanning apparatus is problematic in that, since the LD array 211 is arranged within the image head 210 in a row along a longitudinal direction of the photosensitive drum 200, only one line can be printed at a time. Further, there is a problem in that, if the transfer speed of the image head is increased, the costs of related parts are increased and the resolution is deteriorated. Further, there is an attempt to widen a space for receiving LDs in the image head to allow an LD array to be extended and arranged along the longitudinal direction of the photosensitive drum. However, this attempt is problematic in that the increase in the number of LDs becomes a factor in increasing costs, and the assembly precision of the LD array is decreased, thus the performance of a printer is deteriorated.
Consequently, according to the image head print-type light beam scanning apparatus in which the LD array is arranged in parallel with the rotation axis of the photosensitive drum, other efforts to increase a printing speed contain fundamental problems in the aspects of costs, resolution and printer performance.